fix: session_search fallback preview on summarization failure (salvage #3413) (#3478)

* Fix #3409: Add fallback to session_search to prevent false negatives on summarization failure

Fixes #3409. When the auxiliary summarizer fails or returns None, the tool now returns a raw fallback preview of the matched session instead of silently dropping it and returning an empty list

* fix: clean up fallback logic — separate exception handling from preview

Restructure the loop: handle exceptions first (log + nullify), build
entry dict once, then branch on result truthiness. Removes duplicated
field assignments and makes the control flow linear.

---------

Co-authored-by: devorun <130918800+devorun@users.noreply.github.com>

tools/session_search_tool.py

@@ -392,23 +392,30 @@ def session_search(
             }, ensure_ascii=False)
 
         summaries = []
-        for (session_id, match_info, _, _), result in zip(tasks, results):
+        for (session_id, match_info, conversation_text, _), result in zip(tasks, results):
             if isinstance(result, Exception):
                 logging.warning(
                     "Failed to summarize session %s: %s",
-                    session_id,
-                    result,
-                    exc_info=True,
+                    session_id, result, exc_info=True,
                 )
-                continue
-            if result:
-                summaries.append({
+                result = None
+
+            entry = {
                 "session_id": session_id,
                 "when": _format_timestamp(match_info.get("session_started")),
                 "source": match_info.get("source", "unknown"),
                 "model": match_info.get("model"),
-                    "summary": result,
-                })
+            }
+
+            if result:
+                entry["summary"] = result
+            else:
+                # Fallback: raw preview so matched sessions aren't silently
+                # dropped when the summarizer is unavailable (fixes #3409).
+                preview = (conversation_text[:500] + "\n…[truncated]") if conversation_text else "No preview available."
+                entry["summary"] = f"[Raw preview — summarization unavailable]\n{preview}"
+
+            summaries.append(entry)
 
         return json.dumps({
             "success": True,